The present invention relates generally to the field of oil and gas drilling and more particularly to a method of and system for building structures and drilling oil and gas wells in arctic, inaccessible or environmentally sensitive locations without disturbing the ground surface as in conventional land drilling operations.
The drilling and development of land oil and gas wells require a designated area on which to locate the drilling rig and all the support equipment. Usually drilling locations are reached by some type of road or other access. In rare situations, access is via airlift, either by helicopter, fixed wing aircraft, or both.
Many areas of the world that have potential for oil and gas exploration and development are constrained by special circumstances that make transportation of drilling equipment to a drilling site difficult or impossible. For example, oil and gas may be found in terrain with near-surface water accumulations, such as swamps, tidal flats, jungles, stranded lakes, tundra, muskegs, and permafrost regions. In the case of swamps, muskegs and tidal flats, the ground is generally too soft to support trucks and other heavy equipment. In the case of tundra and permafrost regions, heavy equipment can be supported only during the winter months.
Additionally, certain regions where oil and gas may be found are environmentally sensitive, such that surface access by transporting vehicles can damage the terrain or affect wildlife breeding areas or migration paths. The environmental problems are particularly acute in arctic tundra and permafrost regions. In such areas, road construction is either prohibited or limited to temporary seasonal access.
There are substantial oil and gas reserves in the far northern reaches of Canada and Alaska. However, drilling in such regions presents substantial engineering and environmental challenges. The current art of drilling onshore in arctic tundra is enabled by the use of special purpose vehicles, such as Rolligons(trademark), that can travel across ice roads built on frozen tundra.
Ice roads are built by spraying water on a frozen surface at very cold temperatures. Ice roads are typically 35 feet wide and 6 inches thick. At strategic locations, the ice roads are made wider to allow for staging and turn around capabilities.
Land drilling in arctic regions is currently performed on ice pads, which are typically 500 feet by 500 feet, which for the most part comprises 6-inch thick ice. Typically, the rig itself is built on a 6 to 12-inch thick ice pad. A reserve pit is typically constructed with over a two-foot thickness of ice plus an ice berm, which provides at least two feet of freeboard above the pit""s contents. These reserve pits, which are also referred to as ice-bermed drilling waste storage cells, typically have a volume capacity of 45,000 cubic feet for an estimated 15,000 cubic feet of cuttings and fluid effluent. In addition to the ice roads and the pad, an arctic drilling location typically includes an airstrip, which is essentially an ice road.
The ice roads may be tens of miles to hundreds of miles in length, depending upon the proximity or remoteness of the existing infrastructure. The fresh water needed for the ice to construct the roads and pads is usually obtained from lakes and ponds that are typically numerous in such regions. The construction of an ice road may typically require 1,000,000 gallons of water per mile. Over the course of a winter season, as much as 200,000 gallons per mile may be required to maintain the ice road. Therefore, for a ten mile ice road, a total of 12,000,000 gallons of water would have to be picked up from nearby lakes and sprayed on the selected road bed route. An airstrip may require up to 2,000,000 gallons and a single drill pad may require up to 1,700,000 gallons of water. For drilling operations on a typical 30-day well, the requirement would be approximately 20,000 gallons per day, for a total of 600,000 gallons for the well. A 75-man camp would require and additional 5,000 gallons per day or 150,000 gallons per month. Sometimes, there are two to four wells drilled from each pad, frequently with a geological side track in each well.
In summary, for a winter program of 7 wells, requiring about 75 miles of road, with 7 drilling pads, an airstrip, a 75-man camp and drilling of 5 new wells, plus re-entry of two wells left incomplete, the fresh water requirements could be on the order of 150 million gallons.
Currently, arctic land drilling operations may be conducted only during the winter months. Typically, roadwork commences by the first half of January simultaneously with location building and rig mobilization. Due to the lack of ice roads, initial mobilizations are done with special purpose vehicles such as Rolligons(trademark), approved for use on the tundra. Drilling operations typically commence the first week of February and last until the middle of April, at which time all equipment and waste pit contents must be removed before the ice pads and roads melt. However, in the Alaskan North Slope, the tundra is closed to all traffic from May 15 to July 1 due to nesting birds. If the breakup is late, then prospects can be fully tested before demobilizing the rig. Otherwise all of the infrastructure has to be rebuilt the following season.
From the foregoing, it may be seen that there are several drawbacks associated with current arctic drilling technology. Huge volumes of water are pumped out of ponds and lakes and then allowed to thaw out and become surface run off again. The ice of the roads can become contaminated with lube oil and grease, antifreeze, and rubber products. In addition to environmental impact, the economic costs of drilling in arctic regions is very high. Operations may be conducted only during the coldest parts of the year, which is typically less than 4 or 5 months. Actual drilling and testing may be conducted in a window of only two to four months or less. Therefore, development can occur during less than half the year. During each drilling season, the roads and pads must be built and all equipment must be transported to and removed from the site, all at substantial financial and environmental cost.
The present invention provides a method of and system for drilling wells on land or in relatively shallow water where the rig and drilling facility are elevated above the surface of the ground. The present invention also provides a platform for accommodating other equipment and structures besides drilling equipment. The system of the present invention includes a plurality of platform modules, which are interconnected to one another on site to form a unitary platform structure. The interconnected platform modules are elevated above a surface on plurality of legs coupled to at least some of the platform modules. The elevated interconnected platform modules can support drilling and auxiliary equipment, as well as other structures such as storage structures, living quarters and the like.
The drilling platform modules may be a of a size and shape capable of being transported to a drilling location by aircraft, land vehicles, sleds, boats or barges, or the like. The modules may be configured to float, so that they may be towed over water to the drilling location. Some of the platform modules may comprises structural, weight-bearing members for supporting derricks and heavy equipment, such as drawworks, motors, engines, pumps, cranes, and the like. Others of the platform modules may comprise special purpose modules, such as pipe storage modules; material storage modules for cement, drilling fluid, fuel, water, and the like; and equipment modules including equipment, such as generators, fluid handling equipment, and the like.
The legs are adapted to be driven or otherwise inserted into the ground to support the elevated drilling platform. The legs may comprise sections that may be connected together to form legs of any suitable length. The legs may include passageways for the flow of fluids such as air, refrigerants, cement, and the like. The legs may include a bladder that may be inflated with air or other fluids to provide increased support for the legs.
According to a method of the present invention, a plurality of first drilling platform modules are transported to a first drilling location. The first platform modules may be transportable by aircraft or special purpose vehicles that are adapted to cause minimal harm to the environment. The first platform modules are interconnected to form a first drilling platform. The first drilling platform is then elevated over the first drilling location. Drilling equipment may be installed on the first drilling platform before or after elevation. After installing the drilling equipment, one or more wells may be drilled.
In arctic regions, the modules are transported, and the first platform is built and elevated, during the winter season, while the ground can support vehicles and the equipment. After the platform has been elevated, drilling can continue throughout the year.
In another aspect of the method of the invention, one or more second platform modules may be transported to a second drilling location. The second platform modules are interconnected and elevated to form either a complete second drilling platform or the nucleus for a second drilling platform. When it is desired to drill from the second drilling platform, drilling equipment is transported to and installed on the second drilling platform. The drilling equipment may be transferred from the first drilling platform. Alternatively, the drilling equipment may comprise a second set of drilling equipment transported from a base or other location. The equipment may be used to drill wells from the second platform as part of a multi-season, multi-location drilling program or as a relief well for wells drilled from the first platform.